Because of market constraints, it is becoming economically more attractive to process highly acidic crudes such as acidic naphthenic crudes. It is well known that processing such acidic crudes can lead to various problems associated with naphthenic and other acid corrosion. A number of methods to reduce the Total Acid Number (TAN), which is the number of milligrams of potassium hydroxide required to neutralize the acid content of one gram of crude oil, have been proposed.
One approach is to chemically neutralize acidic components with various bases. This method suffers from processing problems such as emulsion formation, increase in concentration of inorganic salts and additional processing steps. Another approach is to use corrosion-resistant metals in processing units. This, however, involves significant expense and may not be economically feasible for existing units. A further approach is to add corrosion inhibitors to the crudes. This suffers from the effects of the corrosion inhibitors on downstream units, for example, lowering of catalyst life/efficiency. Furthermore, confirmation of uniform and complete corrosion protection is difficult to obtain even with extensive monitoring and inspection. Another option is to lower crude acid content by blending the acidic crude with crudes having a low acid content. The limited supplies of such low acid crudes makes this approach increasingly difficult.
U.S. Pat. No. 3,617,501 discloses an integrated process for refining whole crude. The first step is a catalytic hydrotreatment of the whole crude to remove sulfur, nitrogen, metals and other contaminants. U.S. Pat. No. 2,921,023 is directed toward a method of improving catalyst activity maintenance during mild hydrotreating to remove naphthenic acids in high boiling petroleum fractions. The catalyst is molybdenum on a silica/alumina support wherein the feeds are heavy petroleum fractions. U.S. Pat. No. 2,734,019 describes a process for treating a naphthenic lubricating oil fraction by contacting with a cobalt molybdate on a silica-free alumina catalyst in the presence of hydrogen to reduce the concentration of sulfur, nitrogen and naphthenic acids. U.S. Pat. No. 3,876,532 relates to a very mild hydrotreatment of virgin middle distillates in order to reduce the total acid number or the mercaptan content of the distillate without greatly reducing the total sulfur content using a catalyst which has been previously deactivated in a more severe hydrotreating process.
It would be desirable to reduce the acidity of crude oils without the addition of neutralization/corrosion protection agents and without converting the crude into product streams.